Traceback (most recent call last):
  File "c:\python35\lib\runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "c:\python35\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "C:\Python35\Scripts\mypy.exe\__main__.py", line 9, in <module>
  File "c:\python35\lib\site-packages\mypy\__main__.py", line 7, in console_entry
    main(None)
  File "c:\python35\lib\site-packages\mypy\main.py", line 50, in main
    res = type_check_only(sources, bin_dir, options)
  File "c:\python35\lib\site-packages\mypy\main.py", line 97, in type_check_only
    options=options)
  File "c:\python35\lib\site-packages\mypy\build.py", line 196, in build
    graph = dispatch(sources, manager)
  File "c:\python35\lib\site-packages\mypy\build.py", line 1801, in dispatch
    process_graph(graph, manager)
  File "c:\python35\lib\site-packages\mypy\build.py", line 2044, in process_graph
    process_stale_scc(graph, scc, manager)
  File "c:\python35\lib\site-packages\mypy\build.py", line 2156, in process_stale_scc
    graph[id].write_cache()
  File "c:\python35\lib\site-packages\mypy\build.py", line 1782, in write_cache
    self.manager)
  File "c:\python35\lib\site-packages\mypy\build.py", line 1061, in write_cache
    data = tree.serialize()
  File "c:\python35\lib\site-packages\mypy\nodes.py", line 284, in serialize
    'names': self.names.serialize(self._fullname),
  File "c:\python35\lib\site-packages\mypy\nodes.py", line 2415, in serialize
    data[key] = value.serialize(fullname, key)
  File "c:\python35\lib\site-packages\mypy\nodes.py", line 2356, in serialize
    data['node'] = self.node.serialize()
  File "c:\python35\lib\site-packages\mypy\nodes.py", line 706, in serialize
    'type': None if self.type is None else self.type.serialize(),
  File "c:\python35\lib\site-packages\mypy\types.py", line 47, in serialize
    raise NotImplementedError('Cannot serialize {} instance'.format(self.__class__.__name__))
NotImplementedError: Cannot serialize PartialType instance